Method of and an apparatus for indicating short circuits in the cells of electrolysis plants

ABSTRACT

SHORT CIRCUIT INDICATING DEVICE FOR A CELL OF AN ELECTROLYSIS PLANT WHICH CELL HAS AN ANODE AND A CATHODE, SAID ANODE BEING CONNECTED TO A BUS BAR, WHEREIN A FERROMAGNETIC ARMATURE IS POSITIONED TO BE ATTRACTED ABOUT SAID BUS BAR BY THE MAGNETIC FIELD ABOUT SAID BUS BAR CAUSED BY A SHORT CIRCUIT. PREFERABLY, SAID FERROMAGNETIC ARMATURE IS USED TO ACTIVATE AN ALARM SYSTEM.

Jan. 26, 1971 R, scHAFER 3,559,199

" METHOD OF AND AN APPARATUS FOR INDICATING SHORT CIRCUITS IN THE CELLS OF ELECTROLYSIS PLANTS Filed Aug. 15, 1967 FIG. I

INVENTOR. ROLF SCHA'FER United States Patent s 559 m9 METHOD OF AND ANAPiARATUs FOR INDICAT- ING SHORT CIRCUITS IN THE CELLS 0F ELEC- TROLYSIS PLANTS Rolf Schiifer, Krefeld-Urdingen, Germany, QSSIgHOI' tO Farbenfabriken Bayer Aktiengesellschaft, Leverkusen, Germany, a corporation of Germany Filed Aug. 15, 1967, Ser'. No. 660,815 Claims priority, application Germany, Aug. 18,1966,

F 49,978 Int. Cl. G08b 21/00 U.S. Cl. 340-253 1 Claim ABSTRACT OF THE DISCLOSURE This invention relates to an apparatus for indicating short circuits in the cells of electrolysis plants in which the individual cells or anodes are connected to current leads.

Electrolysis plants are best operated at the lowest possible cell voltage. An important factor in this respect is the loss of voltage in the electrolyte which is minimized by restricting the intervals between the electrodes. Unfortunately, limited intervals between the electrodes increase the frequency with which short circuits occur, .particularly in electrolysis cells where none of the electrodes represents a fixed surface. This applies, for example, to the electrolysis of alkali metal chlorides by the mercury process. The mercury cathode is subject to changes through contamination of the cell base, whilst the graphite anode is as it were used up and has to be continuously reset or adjusted.

If no special safety measures are taken, no short circuits will be noticed until the anode and its lead have been heated to such an extent by the current that smoke is given oft". In most cases, the anode has already been damaged by the time this occurs. Some of the protective coating on the anode rod is destroyed or alternatively the graphite rod cracks. In addition, the soldered connection between the copper rod and the anode rod can be rendered useless, whilst the cover seal or even the base f the cell can be damaged. In either case, an anode of this kind is diflicult to readjust for its entire service life. To prevent an excessive number of short circuits, cells without any protection against short circuits have to be run at a relatively high voltage.

For this reason, so-called unsweat fuses have already been used in plants for the electrolysis of alkali-metal chlorides. A soldered connection is incorporated in the lead or feed band of each individual anode. When the melting point of the solder is exceeded, this soldered connection is broken by spring force, interrupting the flow of current. Unfortunately, these so-ealled unsweat fuses are not free of disadvantages. The unsweat device has to be adapted to the cell load. It mus-t not respond too early because, otherwise, an unnecessarily large amount of work is needed to replace and to repair the melt elements, whilst the danger of a chain reaction becomes too large. In the event of sluggish response, the anode may already have been damaged by the time the flow of current is interrupted. If a plant is to be run under a fluctuating load, favourable adaption is only possible within a certain load range. The capital expenditure on unsweat systems is con "ice siderable because a cell for the electrolysis of alkali metal chlorides may have as many as a hundred anodes, depending on its size. The amount of work involved is also considerable because all fuses which have responded have to be replaced and repaired. In order to screw the leads on again, the cell may have to be switched off altogether, resulting in production losses.

It is already known that a short circuit alarm can be released by measuring the cell voltage. In the event of a short circuit there is a drop in the cell voltage. In the case of cells run at a high current density, however, experience has shown that the fade in voltage is extremely small so that highly sensitive measuring instruments have to be used. In addition, the voltage of the cell is governed by the load. For this reason, it has been proposed automatically to compensate cell voltage and fluctuation in load through cross coil voltme-ters so that all the voltmeters are normally in the neutral position. Only that voltmeter of the cell suffering from a short circuit shows any deflection.

This process also, is attended by a major disadvantage. Since one cell has around one hundred anodes, the short circuit anode has first of all to be detected. This takes so much time that in most cases the anode will already have been damaged by the time it is found.

We have now found that a reliable means of indication can be obtained by using the magnetic field generated around the current lead in the event of cell short circuits if, in accordance with the invention, ferromagnetic armatures provided with elastic reset elements are provided near the current leads. It is largely a question of outlay and usefulness whether indicators of this kind will be provided for groups of anodes or for each individual anode. If, due to a short circuit in a cell, a relatively strong magnetic field is built up around the associated current lead, the ferromagnetic armature kept suspended by the elastic reset member is attracted to the conductor rod. Since, by virtue of the uniform structure of electrolysis plants, the indicators are also distributed uniformly and in a readily seen arrangement at appropriate points throughout the plant it is possible by visual survey of the plant quickly to determine Where an armature has moved into the closed position characteristics of a short circuit. It has even been found that, if the armature is arranged closely adjacent to current feeds, the armature itself, providing it is resiliently suspended in an appropriate manner, will also be laterally deflected towards those current feeds whose associated anodes are affected by the short circuit. It is therefore possible by suitably arranging the armature in dependence upon the design of the electrolysis plant to keep the number down to a minimum without reducing the desired effectiveness in any way.

It is naturally of advantage to design the apparatus according to the invention in such a way that it simultaneously acts as an alarm. According to the invention, this is done by making the ferromagnetic armature the switch of a checking circuit provided with an alarm device. This is achieved with particular advantage if, in addition to the ferromagnetc electrically conductive armature, the elastic reset element too is designed as an electric conductor and connected to an electric lead which is in turn connected with the base of the cell, an alarm device, for example, a Warning device and/or a hooter or horn, being included in the circuit. Thus, in an arrangement of this kind, the cell voltage is used with advantage to actuate the alarm device. It is of course also possible to install a separate circuit. There is of course no need to provide an acoustic alarm for each cell. It is quite sufiicient for one acoustic alarm to be released for the plant as a whole or, if this is too large, for groups comprising a convenient number of cells. Only the optical alarm is preferably separately installed on each cell. To this end, one relay only is included in the primary, optionally fused circuits adjoining the cells, energising the secondary checking circuits provided with the alarm systems. The ferromagnetic armatures are with advantage lined in part at least with a corrosion-resistant material, preferably graphite, on those sides facing the current leads, in order to guarantee effective electrical contact, because ferromagnetic metal, for example, would corrode on account of the vapours present. Similarly, the contact points of the conductor rods may be lined with a corrosion-resistant material. In one particular emobdiment of the apparatus according to the invention, the elastic reset member simultaneously acts as a holder for the armature and consists of a mechanical spring. It is electrically conductive and represents part of the checking circuit.

In the method according to the invention, the armature in the form of a switch is actuated by the magnetic field generated in the event of a short circuit, as a result of which a checking circuit is closed and an alarm system released.

In an alternative method, the short circuit anode is indicated by the magnetic field generated in the event of a short circuit which changes the position of the armature provided with an elastic reset member, the alarm being released through voltage-measuring instruments in a conventional manner.

One embodiment of the invention is diagrammatically illustrated by way of example in the accompanying drawings, wherein:

FIG. 1 shows two ferromagnetic armatures provided with elastic reset elements designed to act as switches; and

FIG. 2 is a circuit diagram for the alarm systems shown in part only for two cells.

As shown in FIG. 1, a plate 2 made of an insulating material is fixed in position near the conductor rail 1. The bending springs 3, carrying the ferromagnetic armatures 5 with their graphite linings 4, are anchored in the bores 6 of the plate 2 and connected with the electrical lead 7 which leads to the base of the cell (not shown).

As shown in FIG. 2, the anodes 8 and 9 of the cell 10 are connected to the rail 12 branched off from the conductor rail 11. A switch 13, which is connected through the lead 14 with the relay 15, is arranged over the rail 12. The lead 14 continues to the base 17 of the cell by way of the fuse 16. The conductor rail 11' leads for the cathode 18 to the cell 10 which is identical in structure with the cell 4 10. The two relays 15 and 15' are connected to two secondary circuits, one of which has a warning light 19 and 19' for each cell, whilst the other has a born or hooter 20 common to all the cells.

I claim:

1. An electrolytic cell comprising a multiplicity of anodes, bus bar means connected to said anodes, electrical power means connected to said anodes through said bus bar and switch means disposed proximate to said bus bar in the vicinity of the electrical connection from said bar to each of said anodes which switch means comprises a conductive contact member attached to a conductive leaf spring member through a ferromagnetic element wherein the spring strength of said leaf spring is sufficient to resist bending thereof by attraction of said ferromagnetic element to said bus bar during passage of normal current quantities through said bus bar but insufficient to resist bending caused by the attraction of said ferromagnetic element by said bus bar on the occasion of increased current passing through said bus bar because of a short circuit in said electrolytic cell between said anode and the cathode thereof; and alarm circuit means electrically connected across said conductive leaf spring and said bus bar activated by contact between said graphite member and said bus bar caused by bending said spring because of said short circuit.

References Cited UNITED STATES PATENTS 1,924,606 8/1933 Hammond 340253 2,410,636 1 1/1946 Cress 340-253 3,121,174 2/1964 Schaefer 340-248 3,200,392 8/1965 Chumakov 340253 2,872,544 2/1959 Hoffman 340'253 3,083,359 3/1963 Smith 335- 17 3,163,801 12/1964 Vansteenkiste 340248 3,240,896 3/1966 Leeds 335-204 ALVIN H. WARING, Primary Examiner D. MYER, Assistant Examiner U.S. Cl. X.R. 

